The invention relates to a mold clamp for an injection molding machine. The mold clamp includes stationary and movable mold clamping plates arranged on the injection molding machine frame. The movable clamping plate is supported on a sliding carriage provided with two sliding blocks and a deflection resistant connecting member. Both mold clamping plates hold the half-molds of the mold and are connectable or connected with each other by cantilever columns or columns that extend therethrough. A mold height adjusting device is provided for adjusting the mold height. For displacing the half-molds of the mold toward and away from each other, there are provided one or more quick-action cylinder units for displacing the movable mold clamping plate to an open or closed position, and a closing cylinder unit for applying a locking or opening force during respective displacement of the movable mold clamping plate.
In injection molding machines which are known in the art, the movable mold clamping plate and the sliding carriage are form-lockingly connected in the vicinity of the machine longitudinal axis near the plate front or rear edge, and are secured to each other, likewise in the vicinity of the longitudinal machine axis, with fastening screws. Such a connection provides only for small displacement of the mold clamping plate relative to the sliding carriage at outer edges to the right and to the left of the mold clamping plate. That is the case when the movable mold clamping plate, viewed from above, deflects relative to the sliding carriage under the action of the closing force of the closing cylinder unit against frictional resistance.
Alignment of the movable mold clamping plate with respect to the stationary mold clamping plate by height and gradient is effected by insertion of shims, the thickness of which is determined experimentally. Sidewise alignment of the movable clamping plate is effected with pressure screws which act sidewise on the sliding carriage. At the four corners of the sliding carriage, combined roller-slide guides are adjusted, with separate pressure screws, on corresponding guide surfaces of the machine frame. The drawback of this lateral guide system is that it is very expensive and imprecise, and the adjusting process is complex and likewise expensive. When the closing cylinder unit applies a closing force to the two half-molds of the mold, the mold clamping plates are subjected to deformations that could have different effects. Dependent on the mold configuration, asymmetrical opening forces occur during mold opening which, with fixed connection between the mold clamping plate and the sliding carriage, results in increased shearing forces acting on the sliding carriage. Thereby, the guides for the sliding carriage in the machine frame are subjected to a high load, which, on one hand, results in wear and harmful play and, on the other hand, in excessive stress of the centering elements of the half-molds.
The tolerances, with which the mold clamping plates, the mold and the guides are encumbered during their manufacturing, are added to the mold joint line and to the guides. With existing unparallelism between the half-molds of the mold, the half-molds will be pulled together to their completely closed position with a substantially excessive force of the closing cylinder. This results in very large shearing forces acting on the guides of the sliding carriage, and they become to some extent deformed and become inclined with respect to the machine frame. Because of this, the lateral guides of the sliding carriage can become so loaded that, on one hand, wear and harmful play occur between the sliding carriage and the machine frame and, on the other hand, the centering elements of the half-mold are again heavily loaded and subjected to wear. Thereby, at a subsequent closing of the mold, the two half-molds are not precisely positioned against each other, due to the unacceptably large play of the sliding carriage, which leads to further damage of the mold. As a result, the quality of the produced molding becomes inferior and leads to so-called floating skin of the molding. With existing unparallelism, the sliding carriage can be further lifted with its front or rear edge on the machine frame until the half-molds are positioned parallel to each other. This leads to a transverse displacement of one half-mold relative to the other with resulting damaging consequences. In the tilted position of the sliding carriage, the mold opens again, and the half-molds are displaced, in this position of the sliding carriage, toward each other to an unprecise position, because of the sliding carriage play, in the injection cycle. This results in tearing of the guide elements of the mold and premature wear. Further, because of the acting shearing forces, additional frictional resistance should be overcome, which should be taken into account when designing the drive.
German Patent 3,718,106 describes a solution to the foregoing problems, according to which the sliding carriage is supported in the machine frame against the action of the vertical load by linear rolling bearing guides. To insure guide parallelism, the sliding carriage is displaced with two synchronously driven threaded spindles.
However, this solution is very expensive and does not solve the problems connected with plan-parallel displacement of both half-molds of the mold.
EP 0 311 133 discloses a different type of mold clamp for small closing forces, which does not include columns. With this mold clamp, all in the vertical direction occurring force differences and position deviations are compensated in the movable mold clamping plate. To this end, the movable mold clamping plate is supported on a rotational horizontal axle and is connected with a hydraulic closing cylinder unit, which centrally engages it, with the axle link. The link has adjustable stops, and the movable mold clamping plate is supported in the machine frame on a roller, whereby angular movement of the link about the rotational axis becomes possible. Below the link, a pull-back spring, acting on the link, is arranged. Besides the shortcoming of this solution being suitable only for small closing forces, the movable mold clamping plate can compensate position deviations between the stationary plate and the movable plate only in the vertical direction. Force differences and position deviations in the horizontal plane, between left and right sides of the apparatus, cannot be compensated.